1. Field of the Invention
The present invention relates to an apparatus and a method for measuring the battery charge level of a portable terminal, and more particularly to an apparatus and a method for measuring the charge level of an main/back-up battery of a portable terminal to which the back-up battery can be fastened.
2. Discussion of the Background
As generally known in the art, recent portable terminals tend to incorporate more functions in order to satisfy ever-increasing user demands. Particularly, portable terminals are expected to incorporate not only functions related to email, Internet, and games, but also multimedia functions for transmitting data and images, which have become popular.
However, this trend has caused a problem in that, although users are provided with various convenient functions, the terminals, particularly their batteries, inevitably consume a large amount of power. This means that user must charge the batteries more frequently.
In an attempt to avoid this problem, it has been proposed that removable back-up batteries, which can be attached to/removed from the terminals as desired, be employed.
When a portable terminal is equipped with a removable back-up battery, the relative potential between the voltage level of the main battery and that of the back-up battery is used to realize a charging/discharging algorithm. This means that, unless the potential of each battery is accurately measured, the charging/discharging algorithm cannot be realized correctly.
For these reasons, when portable terminals are provided with back-up batteries, it is customary to check the voltage level from the output terminal of each battery in order to measure the potential value corresponding to the actual charge levels of the main and back-up batteries.
When main and back-up batteries are connected in parallel and have different potentials, they tend to maintain the same potential. For example, if a main battery having a voltage of 3.4 V is connected in parallel with a back-up battery having a voltage of 3.8 V, the batteries have an average voltage of about 3.6 V. The batteries regain their original voltage levels when disconnected from each other.
In summary, the conventional algorithm has a problem in that it may not be possible to know the exact potential value corresponding to the actual charge level of each battery simply by checking the voltage levels from the output terminals of respective batteries that are connected in parallel.